Embodiments of the present disclosure relate to a fluid extraction system, and more particularly to a fluid extraction system having a control sub-system configured to control a plurality of electric machines.
In oil and/or gas mining operations, an electric machine, such as an electric submersible pump (ESP), is prevalently used to extract production fluids such as oil and/or gas from a well. The ESP may be disposed in the well to remove the oil and/or gas. Conventionally, to control an operating parameter such as an operating speed of the ESP, a variable speed drive (VSD) fed by a fixed frequency alternating current (AC) supply is employed. The VSD synthesizes three-phase AC voltages and currents of such frequency as is necessary to excite the ESP such that the ESP operates in the desired manner.
More particularly, the VSD and a source of the AC supply and are typically disposed on a surface (e.g., outside the well) and the three-phase AC power is delivered into the well to the ESP through a long cable that extends from the surface to a location inside the well where the ESP is deployed. The supply of the AC power into the well is typically very costly as more conductors are needed to supply the three-phase AC power in comparison to the conductors required for the supply of the DC power.
For increased well productivity, it is desirable to have multiple electric submersible pumps within the same well, each operable at its own speed. Accordingly, a well may be formed to have one or more vertical sections and horizontal sections. One or more ESPs may be employed in each of the vertical sections and horizontal sections. Accordingly, if the abovementioned conventional approach is used, an individual VSD may be required for each ESP of the one or more ESPs. Moreover, a separate power cable (containing at least three conductors for three phase AC power) is required to supply the AC three-phase power to each ESP. Accordingly, use of such conventional approach is not cost effective.
In another conventional approach, a common VSD is employed to control operation of the multiple ESPs. However, in such configuration, all the ESPs need to operate at the same operating speed. This is unlikely to optimize the well productivity.
In yet another conventional approach, a single VSD is employed on the surface that supplies AC power to a first ESP in the well, with subsequent ESPs being supplied by controllers that are in the well. These controllers need to function as cyclo-converters that receive an AC of one frequency and amplitude into another AC of another frequency and amplitude for excitation of each additional ESP in the well. However, use of such electronic controllers may not be reliable in the harsh environment within the well. In addition, control of the operating speed of an ESP independent of the operation of other ESPs in the well, is another challenge.